[dspillett]

> what customers SAY they want doesn't necessarily corellate with what they will actually use

A key cause of this in many cases is that the stake-holders you talk to do not work closely with the end users of the system. Talking to the right people can help a lot, though unfortunately as a 3rd party this is not usually anywhere near your realm of control.

The other issue is them knowing what they have and wish to store, but not knowing what outputs are going to be needed down the line. That is harder to fix, but having some good industry knowledge within your company can be a great help on such matters – you can then sometimes preempt client needs if the people holding that knowledge are keeping an active eye on changes (for instance new/planned regulations that might be coming into force in X weeks/months/years).